As you can see, it did turn out to be hardware, a GPU and CPU (ouch!). The flash storage was not it, but I figured that out eventually. This has been an issue since October! With many fixes attempted. It was a bit of a blow to my pride eventually having to turn to Apple, but they stepped up and got it done with only mild frustration on my part. Plus, they picked up the tab as my warranty is certainly expired. There comes a time when you realize that a fix would require more parts then you had at hand. I have been enjoying my functional desktop again, just in time for the new iMac Pro to make it obsolete.